Process for the production of titanium tetrachloride

ABSTRACT

1. IN A PROCESS FOR THE CONTINUOUS PRODUCTION OF TITANIUM TETRACHLORIDE, WHEREIN A FINELY DIVIDED BED OF A TITANIUM MINERAL AND COKE IS MAINTAINED IN A REACTOR, CHLORINE CONTAINING GAS IS INTRODUCED CONTINUOUSLY INTO THE LOWER PORTION OF SAID BED SO AS TO MAINTAIN THE SOLIDS IN SAID BED IN A FLUIDIZED STATE AND CONTINUOUSLY TO REACT WITH THEM, THUS PRODUCING GASEOUS REACTION PRODUCTS INCLUDING TITANIUM TETRACHLORIDE VAPOR, AND A CONTINUOUS STREAM OF SUCH GASEOUS REACTION PRODUCTS WITH SOLID FINES ENTRAINED THEREIN IS CONDUCTED FROM AN UPPER REGION OF THE REACTOR INTO A SEPARATOR IN WHICH SOLID FINES ARE CONTINUOUSLY SEPARATED AND COLLECTED FROM SAID STREAM, THE IMPROVEMENT WHICH COMPRISES CONTINUOUSLY PASSING THE FINES COLLECTED BY SAID SEPARATOR DIRECTLY BACK INTO THE REACTOR BY GRAVITY FLOW THEREOF THROUGH A DOWNWARDLY EXTENDING CONDUIT THAT OPENS INTO SAID REACTOR AT A LEVEL THEREIN WHERE THE GASES THEREIN CONSIST SUBSTANTIALLY ENTIRELY OF SAID GASEOUS REACTION PRODUCTS, WHILE PASSING CONTINUOUSLY FROM THE REACTOR THROUGH SAID CONDUIT, COUNTERCURRENT TO THE RETURNING FINES, A LIMITED FLOW OF SAID GASES SUFFICIENT TO PREVENT CLOGGING OF SAID CONDUIT BY SAID FINES.

Nov. 12, 1914 ms ETAL 3,848,051

PROCESS FOR THE PRODUCTION OF TITANIUM TETRACHLORIDE Original Filed Aug.31, 1967 11v vENTofis ROBERT JEANM/Js ANDRE LOU/5 MICHAUD BY ATT R N EYUnited States Patent O Int. Cl. 601 23/04 US. Cl. 423-79 4 ClaimsABSTRACT OF THE DISCLOSURE The chlorination of titanium minerals andcoke to give titanium tetrachloride using a fluidised bed is carried outin apparatus comprising a cyclone or other separator in the outlet line,a conduit leading from the separator back to the reactor for recyclingfines separated in the cyclone, and a diaphragm in the conduit of opencross-sectional are at most 4, preferably to that of the outlet linefrom the reactor to the cyclone.

This application is a continuation of application Ser. No. 664,665,filed Aug. 31, 1967 and now abandoned.

This invention relates to apparatus suitable for carrying out gas-solidreactions in which the solid reactant or reactants are in the form of afluidised bed, in particular the production of titanium tetrachloride bythe reaction of chlorine with a titanium mineral, e.g. rutile orilmenite or a concentrate of some form of titanium dioxide, and coke orother carbonaceous material.

In such processes the titanium dioxide material usually has a particlesize of 0.25-0.05 mm., and the coke a particle size of 3.15-0.10 mm.However, as a result of the reactions occurring and of abrasion there isformed a certain amount of finely divided material or fines, which isentrained with the gases leaving the reactor. This can represent asubstantial loss of valuable material, as well as giving rise todifliculties and abrasion in subsequent operations, and variousproposals have been put forward for reducing or mitigating the effectsof such entrainment.

One such proposal has been to limit the amount of the solid particlesentrained by increasing the height of the reactor, but this increasesthe capital cost without completely solving the problem.

Attempts have been made to remove the entrained particles from the gasesissuing from the reactor and to recycle them. Thus it has been proposedto introduce into the circuit for the removal of the gases devices forseparating solid constituents such as filters, cyclones, electrostaticprecipitators, etc. If the solids are elfectively recovered in largemeasure they still have to be recycled, and this requires periodicalemptying of the recovery apparatus, and sometimes treatments such aswashing or grading before the recovered product or products can berecycled with fresh material.

All these periodical operations, which require additional capitalinvestment and manual labour, present even greater difficulties when thereaction takes place at a higll temperature as does the production oftitanium tetrachloride, and necessitates the handling of hot productsand often loss of their useful heat if the fresh products are introducedinto the reactor at ordinary temperature.

It is an object of the invention to provide an improved apparatus inwhich these various disadvantages are mitigated or avoided, and whichcan be operated on a continuous basis without external intervention, andis compact and relatively low in cost.

In one aspect the invention consists in apparatus suit- 3,848,051Patented Nov. 12, 1974 able for use in the production of titaniumtetrachloride by the reaction of chlorine with a fluidised bed of atitanium mineral and coke, which comprises a reactor provided with a gasinlet and means for forming a fluidised bed of solid particles by theaction of incoming gas, an outlet for gases from the reactor, meanscommunicating with said outlet for separating solid particles from a gasin which they are entrained, a conduit adapted to feed separated solidparticles from the said separating means back to the reactor, and insaid conduit a diaphragm having an opening of cross-sectional area lessthan A of that of the said gas outlet from the reactor.

The invention consists also in the production of titanium tetrachlorideusing such apparatus.

The invention is illustrated in, and will be described in more detail byreference to, the accompanying drawings, in which:

FIG. 1 is a schematic elevation view of a reactor, including a solids(fines) recovery section, of known type;

FIG. 2 is a large scale view in section of a detailed modification ofthe reactor of FIG. 1, in accordance with the invention;

FIG. 3 is a similar view of another such modification; and

FIG. 4 is a similar view of yet another such modification.

Referring now to the drawings, the apparatus of FIG. 1 comprises afluidised bed reactor 1, shown as containing solid particles 2,generally of small or very small particle size, for example from 50 to6000 microns. Gases are introduced into the reactor 1 through thepipeline 3 at a suflicient rate to allow the solid particles 2 to befluidised, that is to say to maintain them in turbulent agitation over awell defined and practically constant depth. The gaseous products of thereaction, and solids entrained therein, leave through an outlet line 4and pass to a cyclone (or other type of separator) 5, in which theentrained solids are separated from the gases. These solids collect atthe bottom 6 of the cyclone, whence they are returned to the reactorthrough a conduit 9. The gases freed from the solid particles are thenpassed to subsequent treatments through a pipeline 7. The heat losses incyclone 5 are normally sufficiently low to prevent changes intemperature bringing about changes in the composition of the gases, forexample by partial or total condensation of one or more componentsthereof. Thus the solids separated by the cyclone 5 can be continuouslyreintroduced into the reactor 1 without any risk of condensation such ascould cause obstruction.

A diaphragm 10 is inserted in the conduit 9. Its role is to restrict thepassage of gases from the reactor 1 through the conduit 9 instead ofthrough the pipeline 4. A major outflow of gas through pipeline 9 wouldseriously interfere with the functioning of the cyclone, and preventefficient separation of the solids.

Since the amounts of gas passing through pipelines 4 and 9 respectively,are substantially proportional to the cross-sectional area of pipeline 4and to the open area of diaphragm 10, provided the open area of thediaphragm 10 is small, the functioning of the cyclone is no longerdisturbed even though the flow of tines through the recovery section iscontinuous.

The conduit 9 may open into the body of the reactor below the uppersurface 11 of the fluidised bed, and this has the advantage that thefine recycled particles cannot be immediately re-entrained by the streamof gas leaving the reactor. Preferably, however, the said opening isslightly above the surface 11 (as shown in FIG. 1) so that gasesescaping from the reactor through the conduit 9 will not containchlorine to be used in the reaction, which would thus be lost to thereaction and would interfere With subsequent operations.

The gases leaving the reactor 1 through the outlet line 4 are a mixtureof permanent gases, carbon monoxide and carbon dioxide (no chlorineremains above the sur- {face 11), heavy vapours which are easilycondensable, mainly of manganese, zirconium, ferrous and ferricchlorides, and vapours which are more diflicult to condense, namelytitanium and silicon tetrachlorides (about 45% of the total). Theoperating temperature in the reactor 1 is about 1000 C. and ismaintained without supplying external heat because the chlorination isexothermic. At this temperature the vapour pressure of the heavychlorides is sufficiently high for them to be vaporised. A substantialreduction is temperature would produce a reduction in vapour pressureand hence a partial condensation of the heavy chlorides, which couldproduce seizing-up of the cyclone or blockages of the lines.

Experiments have shown that the use of a cyclone and of tubes of arefractory material of as low an external surface area as possible, sothat heat losses can be kept sufficiently low to maintain thetemperature of the recycled particles above 800 C., makes it possible toavoid any condensation of ferrous or other heavy metal chloride, and torecover the entrained fines of coke and of rutile in the form of afree-flowing powder without the formation of agglomerates.

The powder run out from the cyclone in this way is immediately recycledto the reactor 1 without interrupting the operation of the cyclone andpractically without heat losses, in contrast to the standard processesused before the invention.

Further-more, depending on the diameter of the diaphragm 10, a smallfluidised bed can form at the diaphragm, which further tends to reducethe escape of gases from the reactor 1 through the conduit 9.

The diaphragm 10 may be situated anywhere between the base 6 of thecyclone and the opening of conduit 9 into the reactor 1; it isadvantageously placed in a vertical part of the conduit 9, for exampleclose to the cyclone.

The form of the diaphragm 10 may be very simple, and some possible formsare shown in FIGS. 2 to 4, purely by way of example. FIG. 2 shows adiaphragm with a cylindrical orifice 12, while the diaphragm shown inFIG. 3 has a tapered orifice 13. The diaphragm of FIG. 4 resembles thatof FIG. 3, but is surmounted by a sleeve 14 with a tapered orifice 15extending the orifice 13. These various forms are particularly designedto avoid any possi bility of blockage of the diaphragm 10. However otherforms are generally equally suitable, since the risk of blockage is veryslight because of the stream of gas which passes upwards through thediaphragm and may, as already described, form a fluidised mass of thefines above it. Preferable forms of the diaphragm are a truncated coneand a double truncated cone.

The diaphragm 10 may conveniently be positioned between two flanges 16of the conduit 9 (FIGS. 3 and 4).

The area of the opening of the diaphragm depends on the cross-sectionalarea of the main outlet pipeline 4, and will generally be betweenone-fiftieth and one-tenth thereof. Experiments carried out have shownthat if this ratio is greater than 1:4 the operation of the cyclone isfor practical purposes no longer satisfactory, and if it is less than1:200 the flow of the fines down the conduit may be seriouslyobstructed.

The material of the diaphragm 10 must resist corrosion and the hightemperature prevailing in the cyclone. It may be a metal or a mixture ofmetals, refractory brick, concrete, etc. The diaphragm 10 may beintegral or consist of several assembled parts.

To show the advantages of a reactor according to the invention therewill now be described, in a first Example, a standard industrial processfor the preparation of titanium tetrachloride by chlorination, and in asecond Example, the same process carried out in a reactor according tothe invention.

EXAMPLE 1 A mixture of 30% of coke (particle size 0.3-0.1 mm.) and 70%of rutile (particle size 0.1-0.05 mm.) is introduced into a standardchlorinator of internal diameter 140 cm. and height 460 cm., having achlorine-resistant refractory lining.

The fluidisation bed is 150 cm. deep. 980 kg./hr. of titaniumtetrachloride are produced, and its vapours mixed with coke and rutilefines pass into a cyclone which is periodically discharged manually, thefines being recycled with the fresh material fed to the chlorinatorafter being washed with water, graded and dried.

After one weeks running the yield from the rutile establishes itself atan average of 88%, being generally between 83 and 92% depending on therunning conditions, so that the average loss of rutile is 12% EXAMPLE 2The same manufacture as in Example 1 is carried out in a reactor similarto that of FIG. 1, with the diaphragm of FIG. 3. While the dimensions ofthis chlorinattor reactor are the same as in Example 1, the output ishigher at 1470 kg./hr. of titanium tetrachloride. The diameter of theoutlet line 4 is 300 mm, and that of the opening of the diaphragm 10 ismm.

During 12 days running neither the cyclone 5 nor the diaphragm 10 northe conduit 9 were blocked at any time.

Despite the increase in output the yield from the rutile establishesitself at an average of 98%, with maximum variations between 96 and 99%.Thus the average loss has been reduced to 2%, which is due toexceedingly fine particles which cannot be stopped by the cyclone. Theaverage gain over the known method is thus 10%, and also externaloperations are eliminated. With the conduit 9 opening out above the bed,the yield based on the chlorine charged is unchanged and remains at100%, as in Example 1.

The recycling of the fines at a high temperature eliminates heat losses,and does not interfere with the operation of the fluidiser.

The entire apparatus can be run independently and continuously withoutexternal manual intervention.

Although in Example 2 the dimensions of the chlorinator 1 are the sameas in Example 1, the height above the fluidisation bed can very well bereduced, since entrainment of solid particles need no longer be keptdown. Such a reduction in the height of the reactor naturally permits aconsequent reduction in capital and maintenance costs.

The almost complete elimination of solid dusts which are generallyabrasive considerably reduces Wear from abrasion of equipment locatedbeyond the cyclone.

We claim:

1. In a process for the continuous production of titanium tetrachloride,wherein a finely divided bed of a titanium mineral and coke ismaintained in a reactor, chlorine con.- taining gas is introducedcontinuously into the lower portion of said bed so as to maintain thesolids in said bed in a fluidized state and continuously to react withthem, thus producing gaseous reaction products including titaniumtetrachloride vapor, and a continuous stream of such gaseous reactionproducts with solid fines entrained'therein is conducted from an upperregion of the reactor into a separator in which solid fines arecontinuously separated and collected from said stream, the improvementwhich comprises continuously passing the fines collected by saidseparator directly back into the reactor by gravity flow thereof througha downwardly extending conduit that opens into said reactor at a leveltherein where the gases therein consist substantially entirely of saidgaseous reaction products, while passing continuously from the reactorthrough said conduit, couutercurrent to the returning fines, a limitedflow of said gases sufiicient to prevent clogging of said conduit bysaid fines.

2. In a process according to claim 1, restricting said countercurrentflow of said gases through said conduit to a substantially constantamount thereof that is between 5 and A of the amount of said gaseousreaction products being conducted into said separator in said stream.

3. A process for the continuous production of titanium tetrachloride bythe reaction of chlorine with a titanium mineral in the presence of cokein a fluidized bed with continuous recycle to the fluidized bed of finesseparated from the gaseous reaction products wherein the titaniummineral and coke are introduced into a fluidized bed reactor, afluidized bed of the titanium mineral and coke established, molecularchlorine introduced into the fluidized bed, the titanium mineralchlorinated in the fluidized bed with the molecular chlorine to producetitanium tetrachloride as a gaseous reaction product, the gaseousreaction product including titanium tetrachloride and solid finesentrained therewith removed from the reactor via an exit conduit, thegaseous reaction products separated from the solid fines in a separator,the gaseous reaction products recovered to continuously provide titaniumtetrachloride, the separated solid fines continuously recycled to thereactor via a recycle conduit leading from the separator and openinginto the reactor at a level above the operating level of the uppersurface the fluidized bed and having located in it a non-adjustablefluid flow restriction device, allowing gaseous reaction products fromthe fluidized bed to pass through the recycle conduit from the reactorto the separator in a direction of flow opposite to that of therecycling fines and establishing in the recycling fines a fluidized bedin the region immediately upstream (from the gas flow view point) of thefluid flow restriction device.

4. A process according to claim 3 in which the fluid flow restrictiondevice is a diaphragm having an aperture of cross-sectional area betweenA and of the crosssectional area of the exit conduit from the reactor.

References Cited UNITED STATES PATENTS 2,701,179 2/1955 McKinney 23872,745,725 "5/1956 Ward et a1 23-288 2,799,558 7/ 1957 Smith et a1 23-284GEORGE O. PETERS, Primary Examiner U.S. Cl. X.R. 423492

1. IN A PROCESS FOR THE CONTINUOUS PRODUCTION OF TITANIUM TETRACHLORIDE,WHEREIN A FINELY DIVIDED BED OF A TITANIUM MINERAL AND COKE ISMAINTAINED IN A REACTOR, CHLORINE CONTAINING GAS IS INTRODUCEDCONTINUOUSLY INTO THE LOWER PORTION OF SAID BED SO AS TO MAINTAIN THESOLIDS IN SAID BED IN A FLUIDIZED STATE AND CONTINUOUSLY TO REACT WITHTHEM, THUS PRODUCING GASEOUS REACTION PRODUCTS INCLUDING TITANIUMTETRACHLORIDE VAPOR, AND A CONTINUOUS STREAM OF SUCH GASEOUS REACTIONPRODUCTS WITH SOLID FINES ENTRAINED THEREIN IS CONDUCTED FROM AN UPPERREGION OF THE REACTOR INTO A SEPARATOR IN WHICH SOLID FINES ARECONTINUOUSLY SEPARATED AND COLLECTED FROM SAID STREAM, THE IMPROVEMENTWHICH COMPRISES CONTINUOUSLY PASSING THE FINES COLLECTED BY SAIDSEPARATOR DIRECTLY BACK INTO THE REACTOR BY GRAVITY FLOW THEREOF THROUGHA DOWNWARDLY EXTENDING CONDUIT THAT OPENS INTO SAID REACTOR AT A LEVELTHEREIN WHERE THE GASES THEREIN CONSIST SUBSTANTIALLY ENTIRELY OF SAIDGASEOUS REACTION PRODUCTS, WHILE PASSING CONTINUOUSLY FROM THE REACTORTHROUGH SAID CONDUIT, COUNTERCURRENT TO THE RETURNING FINES, A LIMITEDFLOW OF SAID GASES SUFFICIENT TO PREVENT CLOGGING OF SAID CONDUIT BYSAID FINES.